After transfering zabbix-web-mysql to IIS, I got this error:

Locale for language "ru_RU" is not found on the web server.

But russian translate working.
After some debuging I found this, in file ./include/locales.inc.php(95):

if ((stristr($_SERVER['SERVER_SOFTWARE'], 'win32') !== false) || (stristr($_SERVER['SERVER_SOFTWARE'], 'win64') !== false)) {

$_SERVER['SERVER_SOFTWARE'] defined as "Microsoft-IIS/8.5".
So, I changed this line to:

if ((stristr($_SERVER['SERVER_SOFTWARE'], 'win32') !== false) || (stristr($_SERVER['SERVER_SOFTWARE'], 'win64') !== false) || (stristr($_SERVER['SERVER_SOFTWARE'], 'Microsoft-IIS/8.5') !== false)) {

And error disappears.
But this time, If I select russian translate in profile, I still got english frontend.